Micro-electromechanical system device

ABSTRACT

A Micro-Electromechanical Systems (MEMS) device ( 100 ) having conductively filled vias ( 141 ). A MEMS component ( 124 ) is formed on a substrate ( 110 ). The substrate has conductively filled vias ( 140 ) extending therethrough. The MEMS component ( 124 ) is electrically coupled to the conductively filled vias ( 140 ). The MEMS component ( 124 ) is covered by a protective cap ( 150 ). An electrical interconnect ( 130 ) is formed on a bottom surface of the substrate ( 110 ) for transmission of electrical signals to the MEMS component ( 124 ), rather than using wirebonds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the U.S. patent application entitled“MICRO-ELECTROMECHANICAL SWITCH,” filed concurrently with the presentapplication, and which has at least one common co-inventor and isassigned to the same assignee as the present application. The relatedapplication is incorporated by reference into the present application.

FIELD OF THE INVENTION

The present invention relates, in general, to Micro-ElectromechanicalSystem (MEMS) devices and, more particularly, to manufacturing MEMSdevices.

BACKGROUND OF THE INVENTION

FIG. 1 illustrates a MEMS device 10 manufactured in accordance with aprior art technique referred to as a glass paste wafer cappingtechnique. In this technique, a plurality of MEMS devices 11 (one shown)are manufactured on a device wafer 12 such as a silicon wafer.Independently, a screen print of glass paste is deposited on a secondwafer 13, which is commonly referred to as a cap wafer. The glass pasteis cured to form spacers 14, which are then aligned and bonded to devicewafer 12. The two wafer combination is then diced by sawing intoindividual devices. A critical limitation of this technique is that thetemperature needed to bond the glass spacers to the device wafer rangesfrom approximately 400 to 500 degrees Celsius (° C.). Temperatures thishigh can easily damage the MEMS device. Another limitation of thistechnique is that it is relatively complicated due to the use of screenprinting and wafer bonding procedures. Complicated processes aretypically less cost efficient because of the added complexity and thelower yield of operational devices.

FIG. 2 illustrates a MEMS device 20 manufactured in accordance with aprior art technique referred to as a cap/cavity technique. In thistechnique, a plurality of MEMS devices 21 (one shown) are fabricated ona device substrate 22, which is then diced into individual or singulateddevice components. Each individual MEMS component is subsequentlyattached to a packaging substrate 23. Packaging substrate 23 istypically ceramic in composition to prevent Radio Frequency (RF) lossesthat are inherent with substrates such as silicon. MEMS device terminals26 are then coupled to package leads 27 via wirebonds 24. Then, the MEMSdevice is hermetically encapsulated with a ceramic cap 28.

One limitation of this technique is that each MEMS device isindividually handled and bonded to packaging substrate 23. If thesacrificial protective layer separating the upper and lower controlelectrodes during fabrication is removed prior to handling, the MEMSdevice becomes extremely fragile and subject to damage during handlingand bonding. If the sacrificial protective layer is not removed prior tohandling and bonding, the processing becomes much more complicated dueto substrate interaction when the sacrificial protective layer is laterremoved. In either case, the effective yield of the manufacturingprocess is adversely impacted. Another limitation of the cap/cavityapproach is that the upper surface of packaging substrate 23 has manytopographic variations which may prevent the creation of a hermetic sealbetween it and cap 28.

A limitation common to both the glass paste wafer capping technique andthe cap/cavity technique is the requirement for wirebonding the MEMSdevice to external leads. An intrinsic limitation of wirebonding is theparasitic inductance inherent in the wirebond. This parasitic inductancedegrades the RF performance of MEMS devices.

Therefore, a need exists to provide a more reliable, cost effective, androbust MEMS device and method of manufacture that overcomes thedeficiencies of the prior techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a MEMS device manufactured in accordance with a priorart technique referred to as a glass paste wafer capping technique;

FIG. 2 illustrates a MEMS device manufactured in accordance with a priorart technique referred to as a cap/cavity technique;

FIG. 3 is a cross-sectional side view of a MEMS device at an initialstage of manufacture;

FIG. 4 is a cross-sectional side view of the MEMS device of FIG. 3 at alater stage of manufacture;

FIG. 5 is a cross-sectional side view of the MEMS device of FIG. 4 at alater stage of manufacture; and

FIG. 6 is a top view of the MEMS device of FIGS. 3-5.

For simplicity and clarity of illustration, elements in the drawings arenot necessarily drawn to scale, and the same reference numerals indifferent figures denote the same elements.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 3 illustrates an initial stage in the manufacture of a MEMS device100. What is shown in FIG. 3 is a cross-sectional side view of apackaging substrate 110 having surfaces 111 and 112 and a plurality ofvias 141 selectively formed therein. Conventional photolithographicmethods may be employed to form vias 141. It should be understood thethat the techniques for forming vias 141 is not a limitation of thepresent invention.

Now referring to FIG. 4, MEMS device 100 is shown at a later stage ofmanufacture. Vias 141 are filled with an electrically conductivematerial such as, for example, copper, gold, aluminum, alloys of copper,alloys of gold, and the like, to form conductively filled vias 140. Itshould be noted that a filled via does not need to be completely filledto be considered a filled via. Rather, a filled via can be partiallyfilled as long as electrical contact can be made from surface 111 tosurface 112.

A conductive layer is patterned on surface 111 of packaging substrate110 to form electrical interconnects 127, 129, and 130, which are inelectrical contact with corresponding conductively filled vias 140.Suitable materials for electrical interconnects 130 include aluminum,gold, copper, nickel, tin, alloys of aluminum, gold, copper, nickel ortin, cobalt, chromium, suicides of tungsten or tantalum, filled epoxies,filled silicones, or the like. It should be understood that electricalinterconnects 130 are an optional feature.

A conductive layer is patterned on surface 112 of packaging substrate110. This conductive layer forms the basis for several of the MEMScomponents 124 such as MEMS switches and MEMS sensors. By way ofexample, the conductive layer may be patterned to form control leads121, transmission terminals 122, control electrode 125, and travel stops123. Control leads 121 are electrically coupled to correspondingelectrical interconnects 130 by conductively filled vias 140. In thisexample, control leads 121 conduct the actuation voltage in the case ofa MEMS switch, which switch may be formed from the conductive layer onsurface 112. Transmission terminals 122 are RF input/output terminals.The thicknesses of each of the traces on surface 112, i.e., controlleads 121, transmission terminals 122, control electrode 125, and travelstops 123 may be the same or different depending on the particularapplication. The thicknesses may be varied by, for example, altering thedeposition of the material forming the conductive layer.

Additionally, a substrate trace 113 may be formed from the conductivelayer patterned on surface 112. Substrate trace 113 is optional and isused for bonding a protective cap 150 to packaging substrate 110 asdescribed with reference to FIG. 5. Further, substrate trace 113 can bemanufactured from either electrically conductive or electricallynonconductive material. Suitable materials for electrical interconnects113 include aluminum, gold, copper, nickel, tin, alloys of aluminum,gold, copper, nickel or tin, cobalt,

FIG. 5 is a cross-sectional side view of MEMS device 100 further alongin manufacture. A center hinge 137 is coupled to substrate 110 via ananchor 131. Anchor 131 is typically a conductively filled via. Centerhinge 137 is electrically connected to a control electrode 132. Controlelectrode 132 is electrically isolated from control electrode 125, butelectrically coupled to at least one of vias 140. By way of example,control electrode 132 is comprised of an electrically nonconductivematerial, i.e., a dielectric material 133 and an electrically conductivematerial 134. A suitable material for dielectric layer 133 is siliconoxide nitride. Preferably, layer 134 is comprised of a metal havingminimum stiffness and a low thermal expansion coefficient such as, forexample, copper, gold, or the like. The geometry of control electrode132 may vary to optimize charge distribution. By way of example, centerhinge 137 and control electrode 132 are formed from the same dielectricand metal layers. The particular materials for layers 133 and 134 arenot a limitation of the present invention.

Control electrodes 125 and 132 form a cantilever structure, whereincontrol electrode 125 is referred to as a lower control electrode andcontrol electrode 132 is referred to as an upper control electrode.

A shorting bar 135 is connected to control electrode 132 for shortingcontrol leads 121 to transmission terminal 122. Thus, shorting bar 135is positioned over control electrode 125 and transmission terminal 122.Because there is metal to metal contact between shorting bar 135 andtransmission terminal 122, it is preferred that shorting bar 135 andtransmission terminal 122 be made of different metals. The differentmetals should each possess a high melting point to reduce stiction andeach should be resistant to oxidation to promote reliability.

A protective cap 150 having a cap bonding layer 151 at the bondingperimeter is placed over MEMS component 120 such that it mates withsubstrate trace 113. Preferably, the composition of substrate trace 113and cap bonding layer 151 are chosen to achieve alloy bondingtherebetween at a temperature less than that of other metals orcomponents of MEMS device 100. In accordance with the present invention,the alloy bonding can be achieved at temperatures ranging fromapproximately 200° C. to 300° C. and more preferably at temperaturesranging from approximately 200° C. to 250° C. It should be understoodthat if a hermetic seal is not desired, cap bonding layer 151 can becomprised of filled epoxies or filled silicones.

Now referring to FIG. 6, what is shown is a top view of MEMS device 100in accordance with an embodiment of the present invention prior tosealing with protective cap 150. FIG. 6 further illustrates substratetrace 113 having a rectangular geometry. It should be understood thatthe geometry of substrate trace 113 is such that it will coincide withcap bonding layer 151. Other suitable geometries for trace 113 andprotective cap 150 which can perform substantially the same sealing orprotective function include square, circular, pentagonal, and the like.

It should be further understood that trace 113 also forms a planarsurface, i.e., a surface without topological deviation, which enhancesthe formation of a hermetic seal with protective cap 150 is attached.

Packaging substrate 110 which has a plurality of hermetically sealed andpackaged MEMS devices 100 is separated into individual devices for testand shipment.

By now it should be appreciated that a MEMS device having a monolithicMEMS component integral with a substrate and a method for manufacturingthe MEMS device that are cost efficient and easily integrable into amanufacturing process have been provided. The assembly and packaging forMEMS devices in accordance with the present invention offers severaladvantages not available with prior art techniques. For example, theMEMS device is fabricated directly from the packaging substrate ratherthan as a separate component which has to be mounted to a packagingsubstrate. Incorporating vias and metal interconnects eliminates theneed for wirebonds, thereby reducing the problems associated withparasitic inductances in RF applications. Moreover, the MEMS device ofthe present invention has a planar surface, which permits hermeticallysealing the MEMS components 124 within a cavity. The elimination ofwirebonds provides for the manufacture of a smaller MEMS device comparedto MEMS devices having wirebonds. In addition, the present inventionallows bonding the protective cap at temperatures lower than otherprocessing temperatures, which reduces the probability of temperaturedamage to the MEMS device.

While specific embodiments of the present invention have been shown anddescribed, further modifications and improvements will occur to thoseskilled in the art. It is understood that the invention is not limitedto the particular forms shown and it is intended for the appended claimsto cover all modifications which do not depart from the spirit and scopeof this invention. For example, other embodiments could be fabricated toinclude one or more passive devices, i.e., capacitors, inductors,resistors, within packaging substrate 110 or between packaging substrate110 and MEMS component 120. Such embodiments would include a morecomplicated network of vias to interconnect the passive components witheach other and with a MEMS component.

What is claimed is:
 1. A Micro-Electromechanical System (MEMS) device,comprising: a substrate having first and second major surfaces; aplurality of conductively filled vias located within a portion of thesubstrate; a first conductive layer over the first major surface of thesubstrate, a first portion of the first conductive layer electricallyconnected to a first of the plurality of conductively filled vias; and amonolithic MEMS component integral with the substrate having a controlelectrode formed on the substrate and extending from the substrate andoverlying a second via of the plurality of conductively filled vias. 2.The MEMS device of claim 1, wherein the first conductive layer furthercomprises a second portion electrically isolated from the first portion.3. The MEMS device of claim 2, wherein the first conductive layerfurther comprises a third portion electrically isolated from the firstand second portions.
 4. The MEMS device of claim 3, wherein the thirdportion is electrically connected to the second via of the plurality ofconductively filled vias.
 5. The MEMS device of claim 2, furtherincluding a protective cap coupled to the second portion.
 6. The MEMSdevice of claim 5, wherein the protective cap comprises a base structurehaving a periphery, wherein walls extend from the periphery.
 7. The MEMSdevice of claim 6, wherein a portion of the walls includes a protectivecap bonding layer.
 8. The MEMS device of claim 7, wherein a material ofthe protective cap bonding layer and a material of the second portionare the same.
 9. The MEMS device of claim 7, wherein a material of theprotective cap bonding layer is selected from the group of materialconsisting of aluminum, gold, copper, nickel, tin, an alloy of aluminum,an alloy of gold, an alloy of copper, an alloy of nickel, an alloy oftin, cobalt, chromium, a silicide of tungsten, a silicide of tantalum,filled epoxies, and filled silicones.
 10. The MEMS device of claim 1,wherein the monolithic MEMS component is a switch having a shorting bar.11. The MEMS device of claim 1, further including a second conductivelayer over the second major surface, wherein a first portion of thesecond conductive layer is electrically connected to at least one of theconductively filled vias.
 12. The MEMS device of claim 1, wherein themonolithic MEMS component is a sensor.
 13. The MEMS device of claim 1,further including a travel stop on the first major surface.
 14. A methodfor manufacturing a Micro-Electromechanical Systems (MEMS) device,comprising: providing a substrate having first and second majorsurfaces; fabricating a plurality of conductively filled vias extendingfrom the first major surface to the second major surface; fabricating aMEMS component on the first major surface, wherein the MEMS componentcomprises a control electrode, a control lead, and a transmissionterminal formed on the first major surface; and coupling a protectivecap to the substrate.
 15. The method of claim 14, further includingforming a substrate trace on the first major surface.
 16. The method ofclaim 15, further including bonding the protective cap to the substratetrace.
 17. The method of claim 16, wherein bonding the protective cap tothe substrate trace includes forming a hermetic seal.
 18. The method ofclaim 14, wherein the protective cap is made from an electricallyconductive material.
 19. The method of claim 14, further includingforming a travel stop on the first major surface.
 20. The method ofclaim 14, further including forming an electrical interconnect on thesecond major surface, the electrical interconnect contacting one of theconductively filled vias.